How does the feeding behaviour of the common forest toad Rhinella henseli (Anura: Bufonidae) vary in space and time? Trophic ecology, chemical and antimicrobial activity

Douglas da Silva Huning
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Abstract

Studies in trophic and chemical ecology, in particular in amphibians, have gained increasing attention in recent years, given that this is the vertebrate group that has suffered the greatest decline in recent years, caused by the degradation of natural ecosystems and emerging diseases. The assessment of food preferences and prey availability between areas and seasons provides important parameters for the understanding of the population dynamics of leaf-litter toads. The study of the secretions of the parotoid macroglands of these toads also provides insights into the role of these secretions in fighting frog pathogens and their potential applications to combat pathogens that are harmful to humans. In the present study, we describe the trophic ecology of Rhinella henseli (Lutz, 1934), and the variation in its diet between seasons and areas. We also attempt to identify the chemical composition of the secretions of the parotoid macrogland found in the parotoid glands and test their potential antimicrobial activity. We sampled two toad populations in the Atlantic Forest of southern Brazil. The composition of the diet was analysed by season (warm vs. cool) and study area, with the prey items being identified to genus, whenever possible, and classified using the Index of Relative Importance. The parotoid secretions were removed manually from the parotoid glands and analysed via HPLC-MS/MS. We ran microdilution and agar plug diffusion tests to assess antimicrobial activity. The principal prey of these toads are large ants, primarily Pachycondyla sp., which vary in abundance between seasons and, to a lesser extent, between areas. We identified 21 chemical compounds, primarily steroidal bufadienolides. One of the populations presented a subset of 14 of these 21 compounds, reflecting the variation in their spatial distribution. These compounds presented anti-pathogenic properties against Candida albicans and, to a lesser extent, Staphylococcus saprophyticus. Our results indicate that the diet of R. henseli varies significantly between areas and seasons, as do the secretions of their parotoid macroglands between areas. The toxins exhibit antimicrobial activity, although the compounds must be tested in isolation to confirm this.
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常见的森林蟾蜍(无尾目:蟾蜍科)的摄食行为在空间和时间上是如何变化的?营养生态学,化学和抗菌活性
营养和化学生态学的研究,特别是两栖动物的研究,近年来受到越来越多的关注,因为两栖动物是近年来由于自然生态系统退化和新出现的疾病而遭受最严重衰退的脊椎动物群体。不同地区和季节间食物偏好和猎物可得性的评估为了解凋落叶蟾蜍种群动态提供了重要参数。对这些蟾蜍的腮腺巨腺分泌物的研究也为这些分泌物在对抗青蛙病原体中的作用以及它们在对抗对人类有害的病原体方面的潜在应用提供了见解。在本研究中,我们描述了henseli Rhinella (Lutz, 1934)的营养生态学,以及它在季节和地区之间的饮食变化。我们还试图鉴定腮腺中发现的腮腺大腺分泌物的化学成分,并测试其潜在的抗菌活性。我们在巴西南部的大西洋森林取样了两个蟾蜍种群。根据季节(温暖与寒冷)和研究区域分析了饮食的组成,尽可能将猎物确定为属,并使用相对重要性指数进行分类。人工从腮腺中取出腮腺分泌物,采用HPLC-MS/MS进行分析。我们进行了微量稀释和琼脂扩散试验来评估抗菌活性。这些蟾蜍的主要猎物是大蚂蚁,主要是Pachycondyla sp.,它们的丰度在季节之间变化,在较小程度上,在不同地区之间变化。我们鉴定出21种化合物,主要是甾体蟾二烯内酯。其中一个居群中有14种化合物,反映了它们在空间分布上的差异。这些化合物表现出对白色念珠菌和在较小程度上对腐生葡萄球菌的抗致病性。结果表明,不同地区、不同季节的汉塞利鼠的食性和腮腺分泌也存在显著差异。毒素具有抗菌活性,但必须对这些化合物进行分离测试以证实这一点。
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